This invention relates to the treatment of chemical wastes to approximately neutral or at least acceptable effluent to sewers, streams, or the like.
In many operations, such as chemical laboratories, chemical manufacturing, metal cleaning and finishing, water treatment, or the like, periodic alternate discharges of strong acid and strong alkalis are necessary. In other similar cases, large volumes of dilute acids and alkalis are discharged in alternation. In many instances, over an extended period of a day, a week, or more, the amount of acid and the amount of alkali are approximately equivalent, that is, if all of the wastes were impounded they would be, to a considerable extent, self-neutralizing. Impounding of large quantities of such wastes in acid-resistant vessels is expensive. Furthermore, these large vessels are located centrally or at a distance from the waste source, and long runs of acid-resistant piping are required at very substantial expense. The mutual neutralization is, of course, generally less expensive than the addition of purchased acid to neutralize alkaline waste when that occurs and purchased alkali to neutralize acid waste when that is flowing. This last procedure, furthermore, requires modulating type chemical feeders for both acid and alkali and extensive instrumentation for control of these. Therefore, despite its disadvantages self-neutralization has been employed.
It will be evident that in this procedure of self-neutralization, large storage spaces are required simply because of the amount of water associated with the waste flows, that is, the size of the storage space is not determined by the amounts of acid or alkali as such. In fact, the volume of storage space required varies inversely with the concentrations involved, more storage space per unit quantity of acid or alkali being required when the concentrations are low. Obviously, the storage space is also determined by the number of cycles desired to be self-neutralized in a given period of time and rate of flow of the liquid waste streams involved.
The ultimate objective of the neutralization is to maintain the ultimate effluent to a sewer or stream acceptable. Generally, relatively low ultimate acidity is permissible, and while greater amounts of alkalinity are often acceptable, there are frequent limitations even on the permissible alkalinity. The net result of this situation, therefore, is not only a requirement for large storage or impounding volume but the provision of acid or alkali feed to achieve a better approach to neutrality than is achieved by the self-neutralizing aspect of the procedure.
In Crits, U.S. Pat. No. 3,062,739, granted Nov. 6, 1962, there is disclosed a method of continuously neutralizing successively generated quantities of acidic and alkaline waste materials comprising the steps of successively passing said acidic and alkaline quantities through the same weak ionic exchanger in the order in which they are generated. The passage of each of said quantities effectively neutralizes that quantity while, at the same time, effectively regenerates said exchanger for use in neutralizing the passage of the subsequently generated quantity of waste material.
The use of weakly acidic cation exchange resins as described in the Crits patent depends upon establishing the volume of weakly acidic resin in the ion exchanger on the basis of the total pounds of acid or alkali fed at any one time.